Morphology of RICE-2

>> Saturday, August 21, 2010

Oryza sativa L.
Local Name: Dhan
English Name: Paddy (Rice)

Rice is grown as a food crop. It is the staple food of more than 60 percent of the world’s population. About 90 percent of all the rice grown in the world is produced and consumed in Asian region. The genus Oryza L. is classified under the tribe Oryzeae, subfamily Oryzoideae, of the grass family Poaceae (Gramineae). This genus has two cultivated species (O. sativa L. and O. glaberrima Steud) and more than 20 wild species are found distributed throughout the tropics and subtropics. The chromosome number of rice (2n) is 24. 

Growth Habit: It is freely tillering annual herb, cultivated or wild, 50-150 cm long but deep water rice may be 5 m. long.

Root: It has fibrous root system. Seminal roots occur at the early stages. Mature roots are also fibrous and produce smaller roots called rootlets. All roots have root hairs to absorb moisture and nutrients. There are two kinds of mature roots:

1. Secondary adventitious roots
2. Adventitious prop roots or prop roots.

Secondary adventitious roots are produced from the underground nodes of young tillers. As the plant grows, coarse adventitious prop roots often form above the soil surface in whorls from the nodes of the culm.

Stem: It is often called culm which is more or less erect and generally 50-150 cm. long and 6-10 mm. in diameter. The jointed stem or culm is made up of a series of nodes and internodes. Young internodes are smooth and solid. Mature internodes are hollow and finely grooved with a smooth outer surface. Generally, internodes increase in length from the lower to the upper portions of the plant. The lower internodes at the plant base are short and thick. The node is the solid portion of the culm. The node or nodal region bears a leaf and a bud. The bud is attached to the upper portion of the node and is enclosed by the leaf sheath. The bud may give rise to a leaf or a tiller. Early tillers arise from the main culm in an alternate pattern. 

Leaf: The node or nodal region of the culm bears a leaf. Leaves are borne alternately on the culm in opposite directions. One leaf is produced at each node. Varieties differ in the number of leaves produced. The topmost leaf below the panicle is the flag leaf. The flag leaf contributes largely to the filling of grains because it supplies photosynthetic products, mainly to the panicle. The leaf sheath and leaf blade are continuous. A circular collar joins the leaf blade and the leaf sheath. The leaf sheath is wrapped around the culm above the node. Leaf blades are generally flat. Varieties differ in blade length, width, thickness, area, shape, color, angle and pubescence. With many parallel veins on the upper surface of the leaf, the underside of the leaf blade is smooth with a prominent ridge in the middle; the midrib. Most leaves possess small, paired ear-like appendages on either side of the base of the blade. These appendages are called auricles. Auricles may not be present on older leaves. Another leaf appendage is the ligule, a papery membrane at the inside juncture between the leaf sheath and the blade. It can have either a smooth or hair-like surface. The length, color, and shape of the ligule differ according to variety. 

Inflorescence: Terminal panicle of spikelets; partly covered by leaf sheath, rachis of panicle slightly angular, glabrous, somewhat hairy at nodes; erect or curved; one to many branches given out from each node, compact or loose. It is 14-42 cm. long with 50-500 spikelets and the base of the panicle is enclosed by a sheath of Flag leaf.
 Spikelets: Spikelets are borne by panicle. Each spikelet later develops to a grain. These spikelets are borne on the primary and secondary branches. These are the basic unit of the inflorescence and panicle. It consists of the pedicel and the floret. The floret is borne on the pedicel. The rudimentary glumes are the laterally enlarged, cuplike apex of the pedicel. The rudimentary glumes are the lowermost parts of the spikelet. During threshing, the rudimentary glumes are separated from the rest of the spikelet. The sterile lemmas are small, bract like projections attached to the floret. The rachilla is a small axis that bears the single floret. It is between the sterile lemmas and the floret. The rachilla, sterile lemmas and the rudimentary glumes all support the floret. The floret includes the lemma, palea, and the flower. The larger protective glume covering the floret is called the lemma and the smaller one is referred to as the palea. Both the lemma and palea have ridges referred to as nerves. The lemma has five while the palea has three nerves. The middle nerve of the lemma can be either smooth or hairy. The lemma has a constricted structure at its end called the keel. In some varieties, the keel is elongated into a thin extension, the awn.

Flowers: The floret contains a flower. The flower consists of a pistil (female organ) and six stamens (male organs).The stamens have two-celled anthers borne on slender filaments. The pistil contains one ovule and bears a double-plumed stigma on a short style. At the flower’s base near the palea are two transparent structures known as lodicules. The lodicules thrust the lemma and palea apart at flowering to enable the elongating stamens to emerge out of the open floret. The lemma and palea close after the anthers have shed their pollen.

Fruit: The dehulled rice grain is called caryopsis which consists of brownish pericarp layers that envelope it. Next to the pericarp layers are the two tegmen layers and the aleurone layers.

Floral formula: Br. % P2 (lodicules) A 3+3 G1


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